Seabirds are highly vocal at breeding colonies, and although they spend most of their life at sea, our understanding of their vocal behaviour away from breeding colonies is limited. Seabird vocalisations are uniquely adapted to communicate both within dense breeding colonies and at sea, but vocalisations likely serve distinct functions and experience different environmental conditions that influence propagation within these distinct contexts. Here, we investigated the vocal behaviour in alcid seabirds (Family Alcidae) on the northeastern coast of Newfoundland, Canada. In Chapter 2, we identified and quantitatively described vocalisations emitted by common murres (Uria aalge) while foraging at sea and qualitatively compared these calls to colony-based repertoires. Four call types were described (‘eng’, ‘arg’, ‘crow’, ‘eur’) and call type assignments were validated using supervised multivariate analyses (random forest) and observer agreement. Three of these call types visually resembled call types previously described at murre colonies with one exhibiting high temporal variation that appeared to grade between different call types. The fourth call type was novel and may only be emitted at sea. Finally, we postulated functions of these four call types at sea based on the behavioural and social contexts in which they were emitted. In Chapter 3, we investigated the presence and ontogeny of individual-specific signatures in razorbill (Alca torda) chick vocalisations used in parent-chick communication at sea. We quantitatively described the individual signatures encoded within ‘departure’ calls of six razorbill chicks during early (3-5 days old) and late (15-19 days old) nestling stages. Calls were reliably assigned to individuals in both stages with similar classification success (early: 66.7%, late: 69.4%), but classification varied considerably among chicks. Temporal attributes had the strongest potential of individual coding (PIC > 1) and the potential to encode identity increased across nestling development, suggesting their importance in signalling identity during fledging and at sea. These findings provide insight into alcid ecology at sea by highlighting the diversity of acoustic signals used by seabirds in this understudied environment and increasing understanding of the acoustic adaptations to specific ecological pressures experienced away from breeding colonies.